IssueTracker

ConstraintLayout version: 2.1.4

Currently, when I specify layout_constraintHeight_percent, the height is calculated not on the basis of the height of the area determined by constrains of the view, but is based on the parent's height. The constraints are simply ignored in the matter of size and are used only to obtain the position. I have no choice except creating a nested ConstraintLayout with proper constraints just to place there one view with a relative height. Such workarounds contradict the philosophy of ConstraintLayout, which encourages to avoid nested layouts.

I understand that changing already existing semantics of app:layout_constraintHeight_default="percent" is impossible, but maybe you could introduce a new value for it, e.g. app:layout_constraintHeight_default="constrained_percent" which will measure the size based on the specified constraints instead of the parent's dimensions.

The original code:

<androidx.constraintlayout.widget.ConstraintLayout
    android:layout_height="300dp"
    android:layout_width="140dp"
    android:background="#777">

    <View
        android:id="@+id/view1"
        android:layout_width="40dp"
        android:layout_height="60dp"
        android:background="#0f0"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintBottom_toBottomOf="parent" />

    <!-- This view's height is based on the parent size, not the constrained area size -->
    <View
        android:id="@+id/target"
        android:layout_width="50dp"
        android:layout_height="0dp"
        android:background="#f00"
        app:layout_constraintHeight_default="percent"
        app:layout_constraintHeight_percent="0.50"
        app:layout_constraintTop_toTopOf="@id/view1"
        app:layout_constraintLeft_toRightOf="@id/view1"
        app:layout_constraintBottom_toBottomOf="@id/view1" />

</androidx.constraintlayout.widget.ConstraintLayout>

The workaround:

<androidx.constraintlayout.widget.ConstraintLayout
    android:layout_height="300dp"
    android:layout_width="140dp"
    android:background="#777">

    <View
        android:id="@+id/view1"
        android:layout_width="40dp"
        android:layout_height="60dp"
        android:background="#0f0"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintBottom_toBottomOf="parent" />

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="@id/view1"
        app:layout_constraintLeft_toRightOf="@id/view1"
        app:layout_constraintBottom_toBottomOf="@id/view1">
        <View
            android:id="@+id/target"
            android:layout_width="50dp"
            android:layout_height="0dp"
            android:background="#f00"
            app:layout_constraintHeight_default="percent"
            app:layout_constraintHeight_percent="0.50"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintBottom_toBottomOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>

</androidx.constraintlayout.widget.ConstraintLayout>